About nine years ago, while contemplating why human faces have become smaller in the brief span of recorded history—too short a time for evolution to explain—[Harvard evolutionary biologist Daniel] Lieberman wondered whether the modern diet of soft food might be a contributing factor. As bones grow, their size and shape respond to biomechanical stresses, so he decided to study the effects of chewing hard versus soft food on the growth and development of the skull in various animal species. In one experiment, he fed soft food to one group of pigs, hard food to another. The stresses of chewing made the upper and lower jaws of the pigs eating hard food grow larger. The study suggested that there is a link between smaller jaws and regularly chewing very high-quality soft food. And humans, he points out, have never had greater access to high-energy processed food than they do now. “I think many people today never have to actually chew anything all day long,” he says. “You can see the effects of that shift in our heads now in terms of molar impactions”—small faces and jaws leave too little room for teeth.
--Jonathan Shaw, Harvard Magazine, on how to make your kid's face look like Arnold Schwarzenegger's